OTTAWA—Canada is formally invoking a 1977 pipeline treaty with the United States in a bid to prevent Michigan from turning off the taps to Enbridge’s Line 5 pipeline. Foreign Affairs Minister Marc Garneau said in a statement Monday that the transit pipeline treaty “guarantees the uninterrupted transit of light crude oil and natural gas liquids between the two countries.” Line 5 carries 540,000 barrels of light crude and natural gas liquids between Wisconsin, and Sarnia, Ont., which the company and other proponents say are a critical energy source in the U.S. Midwest, as well as Ontario and Quebec. But almost a year ago, Michigan Gov. Gretchen Whitmer revoked an easement granted to the pipeline in 1953 which had allowed it to run through the Straits of Mackinac, a water body connecting Lake Michigan and Lake Huron. Citing potential catastrophic environmental consequences if the aging pipeline ruptures, Whitmer gave Enbridge six …